1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) system, and more particularly, to an apparatus for driving an active matrix type LCD panel with a small deviation of feedthrough voltage.
2. Description of the Related Art
Since LCD panels are thinner in size and lower in power consumption with a lower power supply voltage as compared with CRT panels, the LCD panels have recently been applied to personal computers, word processors, color television receivers, and the like.
An active matrix type LCD panel includes a plurality of gate bus lines, a plurality of data bus lines, and a plurality of pixels arranged between the gate bus lines and the data bus lines. Also, each pixel is formed by a liquid crystal cell and a switching transistor which is, in this case, a thin film transistor (TFT). The TFT is connected between the liquid crystal cell and one of the data bus lines, and the gate of the TFT is connected to one of the gate bus lines.
A prior art apparatus for driving the above-described LCD panel, particularly, the gate bus lines, includes a gate bus line driving circuit formed by serially-connected shift registers whose outputs are connected to the gate bus lines. That is, a start pulse, which is in synchronization with a horizontal synchronization signal, is written into the first stage of the shift registers, and the start pulse is shifted through the shift registers. Thus, the shifted start pulse is sequentially applied as a gate pulse to the gate bus lines, and as a result, the gate bus lines are sequentially driven. This will be explained later in detail.
In the above-described driving apparatus, however, a feedthrough voltage of a pixel located near the gate bus line driving circuit is larger than a feedthrough voltage of a pixel located apart from the gate bus line driving circuit. This difference in feedthrough voltage may reduce the duration of the life of the LCD panel by the application of a DC voltage thereto.
In order to reduce the difference in feedthrough voltage, in another prior art apparatus for driving gate bus lines, gate bus line driving circuits are provided on both sides of the gate bus lines (see: JP-A-SHO57-100467). This will also be explained later in detail. In this prior art apparatus, however, the hardware is increased in size.